Display device, display method, and projection type display device

ABSTRACT

Aspects of the invention can provide a display device, a display method, and a projection type display device that allow a characteristic of a display image such as brightness to be continuously changed. The display device can include a light source capable of emitting a plurality of different color lights and a white light, and an optical modulation device for modulating light corresponding to the lights emitted from the light source. The ratio of the period of emitting the white light relative to the total of the periods of emitting the lights from the light source can be variable.

BACKGROUND

Aspects of the invention relate to a display device, a display method,and a projection type display device.

As information equipment has made remarkable developments, there hasbeen an increasing demand for high resolution, less power consuming, andthin image display devices, and search and development are underway toprovide such devices. Among all, a liquid crystal display device canelectrically control the orientation of liquid crystal molecules andchange the optical characteristics, and is expected to be a displaydevice to satisfy the above demand. A projection type liquid crystaldisplay device (liquid crystal projector) that expands and projects adisplay image emitted from an optical system using a liquid crystalvalve on a screen with a projection lens is as an example of a relatedart liquid crystal display device.

The projection type liquid crystal display devices are divided intoso-called three-plate type devices and single plate type devices. In thethree-plate type device, light from the light source is for exampleseparated into three R (red), G (green), and B (blue) color lights, andthree liquid crystal light valves corresponding to these color lightsare used to carry out optical modulation. The single-plate type devicecarries out optical modulation to the color lights using one liquidcrystal light valve. The single plate type display device that uses onlyone liquid crystal light valve has a simple optical system accordingly,and therefore can be compact.

When color display is carried out using a white light source in thesingle-plate, projection type display device, there are two kinds ofsuch display. One is a space divisional type display in which a liquidcrystal light valve including a color filter is used and three dots forR, G, and B form one pixel. The other is a time divisional type displayin which a white light is temporally separated into R, G, and B colorlights using a color wheel or the like, and time divisional driving(color sequential display) is carried out using the liquid crystal lightvalve.

Techniques of irradiating R, G, and B color lights to a light valveusing a light source (such as a light emitting diode (LED)) that emitsthese color lights instead of a white light source and a color filterhave been disclosed. However, the quantity of light emitted from the LEDis less than that of a light source, such as a lamp, and the displayedimage could be dark. An image displayed by the color sequential displaydescribed above can be even darker, and techniques of brighteningdisplayed images have been developed. See, for example, Japanese PatentLaid-Open No. 2002-251175.

In the disclosure of Japanese Patent Laid-Open No. 2002-251175, when animage is brightened based on the display content in a display devicethat carries out color sequential display, the color components of colorlights R (red), G (green), and B (blue) are changed to C (cyan), Y(yellow), and M (magenta).

By the method disclosed by Japanese Patent Laid-Open No. 2002-251175,when the color components are changed (for example from (R, G, B) to (C,Y, M)), change in the brightness of the image can be disconnected. Whenthe brightness change is disconnected in the image, the viewer may findthe displayed image unnatural.

SUMMARY

An aspect of the invention provides a display device, a display method,and a projection type display device that allow a characteristic of adisplay image such as brightness to be continuously changed.

An exemplary display device according to the invention can include alight source capable of time-sequentially emitting a plurality ofdifferent color lights and a white light (a color light W), and anoptical modulation device for modulating light corresponding to thelights emitted from the light source, and the ratio of the period ofemitting the white light relative to the total of the periods ofemitting the lights from the light source is variable.

More specifically, with the display device according to the invention,the ratio of the period of emitting the white light relative to thetotal of periods of emitting the lights from the light source cancontinuously be changed, so that the brightness of the display image cancontinuously be changed.

More specifically, the display of an image by the white light can beadded to the display of images by the color lights, and the brightnessof the displayed image is increased. By changing the ratio of the periodof displaying the image by the white light, the ratio of the brightnessincrease in the displayed image can be changed. More specifically, whenthe ratio of the period of emitting the white light is graduallyincreased, the ratio of the displayed image by the white lightincreases, so that the image displayed is gradually brightened.Meanwhile, when the ratio of the period of emitting the white light isgradually reduced, the ratio of the display image by the white lightdecreases, so that the image displayed is gradually darkened.

Herein, the white light refers to light that includes at least R, G, andB wave lengths, and does not disturb the color balance of the displayedimage (including the range that can be corrected by the opticalmodulation means) or does not let the viewer perceive color imbalance ifany. More specifically, in order to achieve the above-described aspect,the ratio of periods of emitting the plurality of different color lightsand the white light can preferably be adjusted to a prescribed value.

In this way, since the ratio of periods of emitting the plurality ofdifferent color lights and the white light can be adjusted to aprescribed value, the brightness of the displayed image can be adjustedto a prescribed brightness level.

More specifically, in order to achieve the above-described aspect, theratio of the period of emitting the white light may be adjusted based ona video signal input to the display device. In this way, since the ratioof the period of emitting the white light may be adjusted based on theinput video signal, the brightness can be adjusted based on the contentof the displayed image. Therefore, when an image of a bright content isdisplayed, the brightness of the displayed image can be increased, whilean image of a dark content is displayed, the brightness of the displayedimage can be lowered. In other words, the image can be displayed inbrightness suitable for the content of the displayed image.

More specifically, in order to achieve the above-described aspect, adetection device for detecting the ambient brightness may be provided,and the ratio of the period of emitting the white light may be adjustedbased on the output of the brightness detection device. In this way, theratio of the period of emitting the white light can be adjusted based onthe ambient brightness, so that the brightness of the displayed imagecan be adjusted based on the ambient brightness. Therefore, when theambient brightness increases, the brightness of the displayed image canbe increased, while when the ambient brightness is lowered, thebrightness of the displayed image can be lowered, so that the displayedimage can easily be viewed.

More specifically, in order to achieve the above-described aspect, therecan be an input portion for inputting the ratio of the period ofemitting the white light, and the ratio of the period of emitting thewhite light may be adjusted based on a signal input to the inputportion. In this way, the ratio of the period of emitting the whitelight may be adjusted based on the signal input to the input portion,and therefore the brightness of the displayed image can be adjustedusing the input portion. Therefore, the viewer can adjust the brightnessof the image through the input portion, and the brightness of the imagecan be adjusted to the viewer's taste.

More specifically, in order to achieve the above-described aspect, thelight source preferably has light emitting portions that emit theplurality of different color lights respectively. More preferably, thelight emitting portion is a solid light source. In this way, differentcolor lights can directly be emitted from the light emitting portions inarbitrary timings. Therefore, as compared to the combination of a whitelight source and a color wheel, the number of elements is reduced, sothat the light source can be reduced in size.

The use of the solid light source reduces heat generation, for example,as compared to a high pressure mercury lamp, and therefore the inputelectric power can efficiently be converted into light. Therefore, thepower consumption by the light source can be reduced, so that the powerconsumption by the projection type display device can be reduced.

More specifically, in order to achieve the above-described aspect,during the period of emitting the white light, the white light isemitted by simultaneously emitting the different color lights from thelight emitting portions that emit the different color lights. In thisway, the white light is emitted by simultaneously emitting the differentcolor lights, and therefore as compared to the case of separatelyproviding the light emitting portion that emits the white light, thenumber of kinds of the light emitting portions is reduced. Therefore,when the size of the light source is equal, the number of light emittingportions that emit prescribed color lights can be increased for thenumber of emitting portions for the white light that are not necessary,so that the light quantity of the emitted color lights can be increased.When the number of light emitting portions that emit prescribed colorlights is equal, the light source can be reduced in size by the size ofthe light emitting portions that emit the white light that are notnecessary.

More specifically, in order to achieve the above-described aspect, thelight source may include a white light emitting portion that can emitthe white light, and during the period of emitting the white light, awhite light may be emitted from the white light emitting portion. Inthis way, there is the white light emitting portion capable of emittingthe white light, and the white light is emitted from the white lightemitting portion. Therefore, as compared to the case of emitting thewhite light by simultaneously emitting different color lights,fluctuations in the power consumption can be reduced.

More specifically, as compared to the case of emitting the white lightby simultaneously emitting different color lights, the number of lightemitting portions that turn on can be reduced at the time of emittingthe white light, and the light emitting portions substantially as manyas that in the case of emitting the other color lights are turned on.Therefore, fluctuations in the power consumption can be reduced to asmall level.

More specifically, in order to achieve the above aspect, in the displaydevice in which the different color lights are sequentially emitted, thewhite light may be emitted in a part of the sub unit period. In thisway, the white light is emitted in a part of the sub unit period foremitting a prescribed color light, and therefore, the brightness of theimage to be displayed can continuously be changed simply by changing theturning on sequence of the light emitting portions without changing theduration of one unit period and a sub unit period.

For example, unlike the case of adding a sub unit period for emittingthe white light, the duration of the unit period is not changed, andtherefore the cycle of the images to be displayed corresponding to thecolor lights is not extended. Therefore, the images corresponding to thecolor lights hardly look disconnected, so that the picture quality ofthe images can be prevented from being lowered. Unlike the case ofadding the sub unit period for emitting the white light and shorteningthe sub unit periods (by raising the driving frequency) and keeping theduration of the unit period unchanged, the driving circuit for thedisplay device does not have to be changed because the driving frequencyis not changed, and the brightness of the displayed image cancontinuously be changed.

The white light is emitted in a part of the sub unit period for emittingthe prescribed color light, and therefore the white light is irradiatedon a location where an optical modulation pattern corresponding to theprescribed color light is formed by optical modulation means. Therefore,the brightness of the displayed image can continuously be changedwithout forming another optical modulation pattern corresponding to thewhite light.

For example, unlike the case of adding a sub unit period for emittingthe white light, an optical modulation pattern corresponding the whitelight does not have to be formed from a video signal, and therefore thebrightness of the displayed image can continuously be changed withoutchanging the driving circuit for the display device.

More specifically, in order to achieve the above-described aspect, inthe display device in which the different color lights are sequentiallyemitted, when the white light is emitted, a sub unit period for emittingthe white light may be added to one unit period. In this way, the subunit period for emitting the white light is added to the unit period,and therefore an image corresponding to the white light can be displayedby the optical modulation means. Therefore, the brightness of thedisplayed image can continuously be changed based on the content of theimage.

More specifically, the image corresponding to the white light can bedisplayed independently of the images corresponding to the other colorlights, and therefore the brightness in a prescribed region of the imagefor example can be enhanced, in other words, the brightness caneffectively be changed based on the content of the image.

More specifically, in order to achieve the above-described aspect, theduration of said unit period may be unchanged regardless of thepresence/absences of an additional sub unit period for emitting thewhite light. In this way, the duration of the unit period is notchanged, and therefore the cycle of displaying the images correspondingto prescribed color lights is not changed, so that the imagescorresponding to the color lights hardly look disconnected, and thepicture quality of the display image can be prevented from beinglowered.

More specifically, in order to achieve the above-described aspect, theduration of the sub unit period may be the same as that in the casewithout the additional sub unit period for emitting the white light. Inthis way, the duration of the sub unit period is not changed, andtherefore the brightness of the displayed image can continuously bechanged without changing the driving frequency for the display device.

Unlike the case of shortening the duration of the sub unit period andkeeping the duration of the unit period unchanged, the driving frequencyfor the display device is not changed, and therefore the brightness ofthe displayed image can continuously be changed without changing thedriving circuit for the display device.

More specifically, in order to achieve the above-described aspect, theoptical modulation device is preferably a liquid crystal panel. In thisway, by controlling voltage that drives the liquid crystal panel, theratio of light transmitted through the liquid crystal panel(transmittance) or the ratio of light reflected by the panel cancontinuously be controlled about in the range from 0% to 100%.Therefore, the brightness of the displayed image can precisely beadjusted.

A displaying method according to the invention uses a display devicethat can include a light source capable of time-sequentially emitting aplurality of different color lights and a white light, and an opticalmodulation device for modulating light corresponding to the lightsemitted from the light source. The ratio of the period of emitting thewhite light relative to the total of the periods of emitting the lightsemitted from the light source is variable.

More specifically, by the display method according to the invention, theratio of the period for emitting the white light relative to the totalof the periods for emitting the lights from the light source iscontinuously changed, so that the brightness of the displayed image cancontinuously be changed. In other words, in addition to the display ofthe images by the color lights, the image by the white light can beprovided, so that the brightness of the displayed image can beincreased, and the ratio of the brightness increase in the displayedimage can be changed by changing the ratio of display period for theimage by the white light.

A projection type display device according to the invention can includethe display device according to the invention as described above. Morespecifically, the projection type display device according to theinvention includes the above-described display device according to theinvention and can continuously change the brightness of an image to beprojected.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numerals reference like elements, and wherein:

FIG. 1 is a schematic view of a projection type display device accordingto a first exemplary embodiment of the invention;

FIG. 2 is a schematic view of an illuminating device in the projectiontype display device according to the first exemplary embodiment;

FIG. 3 is a block diagram of the configuration of a driving circuit inthe projection type display device according to the first exemplaryembodiment;

FIGS. 4(a) and 4(b) are timing charts for use in illustration of howvideo signals are written and LEDs are turned on;

FIGS. 5 and 6 are histograms showing the distribution of gray levels ofthe video signals;

FIG. 7 shows how a display image is divided into a plurality of regions;

FIG. 8 is a schematic view of another example of the illuminating devicein the projection type display device according to the exemplaryembodiment;

FIGS. 9 and 10 are block diagrams each showing another example of theconfiguration of the driving circuit in the projection type displaydevice according to the exemplary embodiment;

FIG. 11 is a block diagram of the configuration of a driving circuit ina projection type display device according to a second exemplaryembodiment of the invention;

FIGS. 12(a) and 12(b) are timing charts for use in illustration of howvideo signals are written and LEDs are turned on according to theexemplary embodiment;

FIGS. 13(a) and 13(b) are views for use in illustration of how a videosignal corresponding to a color light W is produced;

FIGS. 14(a) and 14(b) are views for use in illustration of how a videosignal corresponding to a color light W is produced;

FIG. 15 is a view for use in illustration of how a video signalcorresponding to a color light W is produced; and

FIG. 16 is a timing chart for use in illustration of how video signalsare written and LEDs are turned on according to the exemplaryembodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

Now, a first exemplary embodiment of the invention will be described inconjunction with FIGS. 1 to 10. Referring to FIG. 1, a projection typedisplay device (display device) according to the first exemplaryembodiment will be described. The projection type display deviceaccording to the exemplary embodiment is a projection type color displaydevice that modulates light emitted from a light source using a liquidcrystal light valve and displays a color image based on the light.

FIG. 1 is a schematic view of the projection type display deviceaccording to the embodiment. As shown in FIG. 1, the projection typedisplay device essentially includes an illuminating device 1 thattime-sequentially emits color lights in colors R, G, B, and W (white), aliquid crystal light valve (light modulating means, a liquid crystalpanel) 40 that modulates the lights in colors R, G, B, and W(hereinafter also as color lights R, G, B, and W) and a projection lens70 that projects the modulated lights.

FIG. 2 is a schematic view of the illuminating device in the projectiontype display device. The illuminating device 1 can include an LED array(light source) 10 that emits color lights R, G, B, and W as illuminatinglight, and an integrator lens system 20 that equalizes the illuminationdistributions of the emitted color lights R, G, B, and W.

As shown in FIG. 2, the LED array 10 can include an LED (a lightemitting portion, a solid light source) 10 r that emits a color light inR, an LED (a light emitting portion, a solid light source) 10 g thatemits a color light in G, and an LED (a light emitting portion, and asolid light source) 10 b that emits a color light in B. These LEDs 10 r,10 g, and 10 b are repeatedly arranged in the vertical direction (thevertical direction in FIG. 2) in this order and columns of the LEDs 10r, 10 g, and 10 b are arranged in the lateral direction (the horizontaldirection in FIG. 2). Between adjacent columns in the lateral direction,the LEDs are arranged shifted by half the interval of the LEDarrangement in the vertical direction so that the LEDs 10 r, 10 g, and10 b can be arranged closely to each other. The LEDs that emit lights inthe same colors are arranged not to be adjacent to each other.

The LED array 10 can supply current to the LEDs 10 r, 10 g, and 10 b atthe same time, so that a color light in W can be emitted from the LEDarray 10 by simultaneously emitting color lights R, G, and B from theLEDs 10 r, 10 g, and 10 b, respectively.

As shown in FIG. 2, in the LED array 10, a plurality of sets of LEDs 10r, 10 g, and 10 b that emit color lights may be provided or one of eachmay be provided.

The integrator lens system 20 can include first and second integratorlenses 21 and 22 provided in this order from the side of the LED array10. The integrator lenses 21 and 22 are formed as a micro lens arrayincluding a plurality of two-dimensionally arranged micro lenses. Thefirst integrator lens 21 divides light (illumination light) emitted fromthe LED array 10 into a plurality of luminous fluxes, and the secondintegrator lens 22 serves as a convoluting lens that convolutes thefluxes in the position of the liquid crystal light valve 40. Ifnecessary, a condenser lens for convoluting a two-dimensional lightsource image may be provided in the position of or succeeding the secondintegrator lens 22. In the following description, the second integratorlens is used as the convoluting lens.

The liquid crystal light valve 40 is made of an active matrix type,light-transmissive liquid crystal panel that has pixels for displayingimages arranged in a matrix. The valve is driven to change thetransmittance of incoming light (to carry out spatial modulation) basedon a processed video signal on a pixel-basis. More specifically, voltageapplied to the light-transmissive electrode of the liquid crystal lightvalve is controlled, so that the light transmittance is controlled inthe range from almost 0% to 100%.

For the liquid crystal light valve 40, active matrix type,light-transmissive liquid crystal cells in TN (Twisted Nematic) modeusing a thin film transistor (TFT) as a pixel switching element areused.

Now, a method of driving a projection type display device according tothe exemplary embodiment will be described.

FIG. 3 is an exemplary block diagram of the configuration of a drivingcircuit for the projection type display device according to theembodiment. As shown in FIG. 3, according to the embodiment, videosignals corresponding to color lights R, G, and B are input parallel toa control portion 81, and a timing signal is also input to the controlportion 81.

The control portion 81 determines the timings of switching on the LEDs10 r, 10 g, and 10 b based on the input video signals. The video signalscorresponding to the color lights R, G, and B input parallel to thecontrol portion 81 are temporarily stored in a frame memory 82, and thevideo signals are sequentially obtained into the control portion 81 inthe order in which they are to be displayed, for example in the order ofthe video signal corresponding to R, the video signal corresponding toG, and the video signal corresponding to B.

The video signals obtained into the control portion 81 are output to theliquid crystal light valve 40 in the order of input, together with thetiming signal, and the liquid crystal light valve 40 controls thetransmittance of light based on the input video signals and forms anoptical modulation pattern. At the same time, the control portion 81switches on the LEDs 10 r, 10 g, and 10 b corresponding to the outputvideo signals through any of the LED drivers 83 r, 83 g, and 83 b anddirects color lights corresponding to the video signals to the liquidcrystal light valve 40. Consequently, the image corresponding to thecolor lights is projected on the screen 71 by the projection lens 70(see FIG. 1).

Now, the relation between the writing of the video signals to the liquidcrystal light valve 40 described above and the turning on of the LEDs inconnection with time will be described with reference to FIGS. 4(a) and4(b). FIGS. 4(a) and 4(b) are timing charts for use in illustration ofhow the video signals are written to the liquid crystal light valve 40and the LEDs are switched on in connection with time.

The turning on timings of the LEDs can be divided into two kinds, one ofwhich is color reproducibility-oriented timing (with no color light Wemitted), and the other is brightness-oriented timing (with color lightW emitted). FIG. 4(a) is for the color reproducibility-oriented method,and FIG. 4(b) is for the brightness-oriented method.

Note that these two kinds of turning on timings may be switched inresponse to a mode switch signal from a mode switch portion (not shown)provided in the projection type display device that allows the viewer toswitch between the color reproducibility-oriented mode and thebrightness-oriented mode. Alternatively, they may automatically beswitched depending on the content and brightness of images to bedisplayed.

Referring to FIG. 4(a), the color reproducibility-oriented turning ontiming will be described. As shown in FIG. 4(a), a color image isdisplayed on the basis of a field (one unit period) consisting of subfields (sub unit periods) displaying images corresponding to R, G, andB. In the field, for example the sub fields corresponding to R, G and Bare arranged in this order.

In the sub fields, video signals Sr, Sg, and Sb for R, G, and B areinput to the liquid crystal light valve. Then, after a writing scanningperiod T1 during which the video signals are sequentially written to theliquid crystal light valve from the top end to the lower end and aresponse waiting period T2 necessary for the liquid crystal in theliquid crystal light valve to respond to the video signals, currentcorresponding to the video signals is supplied to the LEDs and colorlights are irradiated to the liquid crystal light valve for a prescribedperiod.

After the irradiation of the color lights, the next video signals areinput to the liquid crystal light valve, and the next sub field starts.

Now, referring to FIG. 4(b), the brightness-oriented turning on timingwill be described. As shown in FIG. 4(b), the structures of the fieldand the sub fields for displaying a color image are the same as those bythe color reproducibility-oriented turning on timing, and in each of thesub fields, the process from the input of the video signals to thepassage of the response waiting period T2 is the same as that by thecolor reproducibility-oriented turning on timing.

After the response waiting period T2, color lights based on the videosignals are irradiated for a prescribed period shorter than that by thecolor reproducibility-oriented turning on timing. Then, current issupplied to all the LEDs, and a color light W is irradiated to theliquid crystal light valve.

When the irradiation of the color light W ends, the next video signalsare input to the liquid crystal light valve, and the next sub fieldstarts.

As shown in FIGS. 4(a) and 4(b), the durations of the periods for thesub fields and the field are the same in the colorreproducibility-oriented mode and the brightness-oriented mode.

Note that the ratio of the period of irradiating color lights R, G, andB in the sub fields and the period of irradiating the color light W iscontrolled based on an image to be displayed as will be described. Theratio can range from the case of irradiating only the color lights R, G,and B (in FIG. 4(a)) to the case of irradiating only the color light W(for black and white display).

Now, display video adaptive control, in other words, control accordingto which the ratio of period to irradiate the color light W is increasedfor a bright video scene while the ratio is reduced for a dark scenewill be described.

In this case, as described above, the turning on timings for the LEDs 10r, 10 g, and 10 b are determined based on the video signals in thecontrol portion 81, and there may be the following three kinds ofmethods.

(a) In image data included in images in a frame of interest, the graylevel in the maximum brightness is used as a control signal.

Assume for example that there is a video signal including gray levels of256 steps from 0 to 255. Assume that for one arbitrary frame formingcontinuos video, the appearance frequency distribution (histogram) ofeach of the gray levels of the pixel data included in the frame is asshown in FIG. 5. In FIG. 5, the brightest gray level included in thehistogram is 150, and therefore the gray level of 150 is used as acontrol parameter to control the ratio of the period of irradiating thecolor light W. By this method, the brightness can be expressed mostfaithfully to the input video signals.

(b) Based on the appearance frequency distribution (histogram) per graylevel included in a frame of interest, the gray level corresponding to aprescribed ratio (such as 10%) is used as a brightness control signal.

When for example the appearance frequency distribution of the videosignals is as shown in FIG. 6, the region corresponding to 10% from thebrighter side of the histogram is set as the region. If the gray levelcorresponding to the 10% point is 230, the gray level of 230 is used asa control parameter to control the ratio of the period of irradiatingthe color light W. As shown in the histogram in FIG. 6, when there is anabrupt peak near the gray level of 255 and the method (a) is employed,the gray level of 255 is used as a control parameter. Note however thatthe abrupt peak is not much significant as information in the displayedimage as a whole. In contrast, by the method of using the gray level of230 as the control parameter, determination is carried out based on aregion that has a significance as information in the display image as awhole. The ratio may be changed about in the range from 2% to 50%.

(c) A display image is divided into a plurality of blocks, the averageof the gray levels of the pixels included per block is obtained and themaximum value is used as a brightness control signal. As shown in FIG.7, for example, the display image is divided into m×n blocks and theaverage values of the brightness (gray levels) for blocks A₁₁, . . . ,A_(mn) are calculated, and the largest value among them is set as acontrol parameter. Note that the display image is preferably dividedinto about 6 to 200 blocks. By the method, the atmosphere of the displayimage as a whole is not altered and the brightness can be controlled.

Regarding the methods (a) to (c) described above, in addition todetermining the control parameter for the entire display region, themethods may be applied for example to only a particular part of thedisplay region, such as the central part. In this way, the brightnessmay be determined from the part of the image that would attract theviewer's attention. In this way, images corresponding to R, G, and Birradiated with color light W may be inserted in sub fields displayingthe images corresponding to R, G, and B, so that the brightness of thecolor image to be displayed can be increased.

Based on the input video signal, the ratio of the period of irradiatingthe color light W can be adjusted, so that the brightness can beadjusted based on the content of the image to be displayed.

Since lights R, G and B can be emitted directly from the LEDs 10 r, 10g, and 10 b, respectively, the number of components and the size of thelight source can be reduced for example as compared to the combinationof the white light source and the color wheel.

The use of the LEDs 10 r, 10 g, and 10 b can reduce heat generation, forexample, as compared to a high pressure mercury lamp, and thereforeinput electric power can efficiently be converted into light. In thisway, the power consumption by the light source can be reduced, so thatthe power consumption by the projection type display device can also bereduced.

The color light W can be emitted by simultaneously emitting the colorlights R, G, and B, and therefore the kinds of necessary LEDs can bereduced as compared to the case in which an LED for emitting the colorlight W is separately provided. Therefore, when the size of the LEDarray 10 is equal, the number of LEDs 10 r, 10 g, and 10 b that emitcolor lights R, G, and B can be increased by the number of LEDs foremitting the color light W, and the light quantity of the color lightsto be emitted can be increased. On the other hand, when the numbers ofthe LEDs 10 r, 10 g, and 10 b that emit the color lights R, G, and B isequal, the LED array 10 can be reduced in size by the size of the LEDsfor the color light W that are not provided.

The color light W is emitted during a part of sub fields correspondingto color lights R, G, and B, and therefore the duration of one field orone sub field does not have to be changed and the brightness of thedisplay image can continuously be changed simply by changing the turningon sequence of the LEDs. For example, unlike the case in which a subfield for the color light W is additionally provided, the duration ofone field is not changed, and therefore the cycle of displaying imagescorresponding to color lights R, G, and B is not prolonged. Therefore,the images corresponding to the color lights R, G, and B hardly lookdisconnected, so that the picture quality of the images can be preventedfrom being lowered. Unlike the case in which a sub field for the colorlight W is additionally provided and the duration of a sub field isshortened (by raising the driving frequency) while the duration of onefield is kept unchanged, the driving frequency for the projection typedisplay device does not change, and therefore the brightness of thedisplay image can be changed readily and continuously without changingthe driving circuit in the projection type display device.

The LED array 10 may include LEDs 10 r, 10 g, and 10 b that emit colorlights R, G, and B as shown in FIG. 2, while as shown in FIG. 8, an LED10 w (a white light emitting portion, a solid light source) that emitsthe color light W may additionally be provided. In other words, thearray may include the LEDs 10 r, 10 g, 10 b, and 10 w.

In this way, the color light W can be emitted from the LED 10 w, andtherefore as compared to the case in which the color light W is emittedby simultaneously emitting the color lights R, G, and B, the number ofLEDs to turn on in emitting the color light W is reduced, which can keepfluctuations in the power consumption in a small level.

If necessary, the color light W may be emitted together with the colorlights R, G, and B, so that a much brighter image than the case ofemitting only the color lights R, G, and B can be obtained.

The ratio of the period of irradiating the color lights R, G, and B insub fields and the period of irradiating the color light W may becontrolled depending on video to be displayed as described above, whileas shown in FIG. 9, an optical sensor (a brightness detection device)91, such as a CCD (Charge Coupled Device) that detects the ambientbrightness, may be provided, so that the ratio of the period of emittingthe color light W may be controlled based on the output of the opticalsensor 91. In this way, the brightness of a displayed image can beadjusted based on the ambient brightness, so that the displayed imagecan easily be viewed.

As shown in FIG. 10, there may be an input portion 95 that determinesthe brightness of an image to be displayed (the ratio of the period ofemitting the color light W), so that the viewer may input a desiredbrightness level to the input portion 95 and the ratio of period ofirradiating the color light W may be controlled in response to a signaloutput from the input portion 95. In this way, the brightness of thedisplayed image can be adjusted by the input portion 95 based on thesignal output from the input portion 95, so that the brightness of thedisplayed image can be adjusted to the viewer's taste.

Now, a second exemplary embodiment of the invention will be described inconjunction with FIGS. 11 to 15. The structure of the projection typedisplay device according to the exemplary embodiment is the same as thatof the first exemplary embodiment, but the driving method is differentfrom that according to the first exemplary embodiment. Therefore, in thefollowing description of the second exemplary embodiment, only themethod of driving the projection type display device will be describedin conjunction with FIGS. 11 to 15, and the structure of the displaydevice will not be described.

FIG. 11 is an exemplary block diagram of the configuration of thedriving circuit for the projection type display device according to theembodiment. Now, the method of driving the projection type displaydevice according to the embodiment will be described. As shown in FIG.11, according to the exemplary embodiment, video signals correspondingto color lights R, G, and B are input parallel to a control portion 81A,and a timing signal is also input to the control portion 81A.

The control portion 81A produces a video signal corresponding to a colorlight W based on the input video signals (the method of which will bedescribed below), and the timings of turning on the LEDs 10 r, 10 g, and10 b are determined. Then, the video signals corresponding to the colorlights R, G, and B input parallel to the control portion 81A and thevideo signal corresponding to the color light W are temporarily storedin a frame memory 82, and then obtained into the control portion 81A inthe order of the video signal to be displayed, for example in the orderof the video signal corresponding to R, the video signal correspondingto G, and the video signal corresponding to B.

The video signals obtained into the control portion 81A are output tothe liquid crystal light valve 40 together with the timing signal in theorder in which they are obtained, and the liquid crystal light valve 40controls the transmittance of light based on the input video signals andforms an optical modulation pattern. At the same time, the controlportion 81A turns on the LEDs 10 r, 10 g, and 10 b corresponding to theoutput video signals through any or all of the LED drivers 83 r, 83 g,and 83 b and color lights corresponding to the video signals areirradiated to the liquid crystal light valve 40. Consequently, the imagecorresponding to the color lights R, G, B, and W is projected on thescreen 71 by the projection lens 70 (see FIG. 1).

Now, the relation between the writing of the video signals to the liquidcrystal light valve 40 described above and the turning on of the LEDs inconnection with time will be described with reference to FIGS. 12(a) and12(b). FIG. 12(a) is a chart for use in illustration of the relationbetween a field and sub fields in the color reproducibility-orientedmode, and FIG. 12(b) is a chart for use in illustration of the relationbetween a field and sub fields in the brightness-oriented mode.

In the color reproducibility-oriented mode, the relation between thefield and the sub fields is the same as that according to the firstexemplary embodiment and is as shown in FIG. 12(a) and no furtherdescription will be provided about it.

Now, referring to FIG. 12(b), the relation between a field and subfields in the brightness-oriented mode will be described. As shown inFIG. 12(b), a color image is displayed on the basis of one fieldconsisting of sub fields (sub unit periods) that display imagescorresponding to R, G, and B, and a sub field that displays an imagecorresponding to W. One field is made of for example sub fieldscorresponding to R, G, B, and W arranged in this order.

The sub fields corresponding to R, G, and B are the same as thoseaccording to the first exemplary embodiment, and are as shown in FIG.12(b) and no further description will be provided about it.

The sub field corresponding to W starts from the point when theirradiation of the color light B ends and the video signal Sw for W isinput to the liquid crystal light valve. Then, after the writingscanning period T1 and the response waiting period T2, current issupplied to all the LEDs, and the color light W is irradiated to theliquid crystal light valve for a prescribed period. When the irradiationof the color light W ends, the next video signal Sr is input to theliquid crystal light valve and the next sub field is started.

As shown in FIGS. 12(a) and 12(b), the duration of each sub field is thesame in the color reproducibility-oriented mode and thebrightness-oriented mode, and the sub field for displaying the imagecorresponding to W is additionally provided, which extends the period ofone field. In this way, in addition to the sub fields for displayingimages corresponding to R, G, and B, a sub field for displaying an imagecorresponding to W is additionally provided in one field, so that thebrightness of the color image to be displayed can be increased.

Now, a method of producing a video signal corresponding to the colorlight W according to the exemplary embodiment will be described. Asdescribed above, the video signal corresponding to the color light W isproduced based on the video signal in the control portion 81A asdescribed above, and the following two methods may be employed.

(1) The video signals corresponding to R, G, and B are multiplied byprescribed coefficients, and the sum of the results may be used as avideo signal corresponding to W.

As shown in FIG. 13(a), for example, when video signals Sr, Sg, and Sbcorresponding to images in R, G, and B are multiplied by coefficients α,β, and γ, respectively, and the sum of the results is a video signal Swcorresponding to an image in W (Sw=αSr+βSg+γSb), the video signal Swcorresponding to W provides an image as shown in FIG. 13(b). By thismethod, in a sense, the black and white version of the color imageexpressed by the R, G, and B images is attained as an image for W, andthe displayed image as a whole can be brightened depending on thebrightness distribution of the image.

(2) A video signal representing a region in which images correspondingto R, G, and B overlap in the lowest brightness level among the R, G,and B images is attained as a video signal corresponding to W. When forexample images corresponding to R, G, and B are arranged as shown inFIG. 14(a), and the video signals based on which the images aredisplayed in the brightness levels shown in FIG. 15 are input, a videosignal displaying the region Aw in which images corresponding to R, G,and B shown in FIG. 14(b) overlap in the lowest brightness level Lwamong the images R, G, and B shown in FIG. 15 is produced. By thismethod, the region to be originally displayed in white can further bebrightened, and the bright region in the image can further be enhancedin brightness.

In this way, a sub field that emits a color light W is additionallyprovided, so that the image corresponding to the color light W canseparately be displayed. More specifically, the brightness caneffectively be changed based on the content of the image, for examplefor enhancing the brightness in a prescribed region of the image,because the image corresponding to the color light W does not depend onthe images corresponding to the other color lights.

Since the duration of the sub field does not change, the brightness ofthe image to be displayed can continuously be changed without changingthe driving frequency for the projection type display device. Forexample, as compared to the case of shortening the duration of each subfield and keeping the duration of one field unchanged, the brightness ofthe display image can readily be changed continuously because thedriving frequency for the projection type display device is not changedand the driving circuit for the projection type display device does nothave to be changed either.

As described above, the duration of the sub field in the colorreproducibility-oriented mode and the brightness-oriented mode may bethe same or as shown in FIG. 16, the duration of the sub field in thebrightness-oriented mode may be shortened and the duration of the fieldin the color reproducibility-oriented mode and the brightness-orientedmode may be the same. In this way, since the duration of one field doesnot change, the cycle of displaying images corresponding to color lightsdoes not change regardless of whether the color reproducibility-orientedmode or the brightness-oriented mode is employed. Consequently, theimages corresponding to the color lights hardly look disconnected, sothat the picture quality of the images can be prevented from beinglowered.

It should be noted that the technical coverage of the invention is notlimited to the above-described exemplary embodiments, and variousmodifications can be made without departing from the spirit and scope ofthe invention. For example in the above embodiments, the invention isapplied to the projection type display device, but the invention may beapplied to displays of other kinds, such as a direct-view type displaydevice without limiting application to the projection type display.

According to the embodiments, the light transmissive liquid crystallight valve is employed as the optical modulation means, while lightvalves of other kinds, such as a reflection type liquid crystal lightvalve can be employed without limiting application to the lighttransmissive liquid crystal light valve.

While this invention has been described in conjunction with the specificembodiments thereof, it is evident that many alternatives,modifications, and variations will be apparent to those skilled in theart. Accordingly, preferred embodiments of the invention as set forthherein are intended to be illustrative, not limiting. There are changesthat may be made without departing from the spirit and scope of theinvention.

1. A display device, comprising: a light source capable oftime-sequentially emitting a plurality of different color lights and awhite light; an optical modulation device that modulates lightcorresponding to the lights emitted from the light source; and a ratioof a period of emitting the white light relative to a total of theperiods of emitting the lights from the light source being variable. 2.The display device according to claim 1, the ratio of the periods ofemitting the plurality of different color lights and the white lightbeing capable of being adjusted to a prescribed value.
 3. The displaydevice according to claim 2, the ratio of the period of emitting thewhite light being adjusted based on a video signal input to the displaydevice.
 4. The display device according to claim 2, further comprising:brightness detection device that detects an ambient brightness; and theratio of the period of emitting the white light being adjusted based onthe output of the brightness detection device.
 5. The display deviceaccording to claim 2, further comprising: an input portion that inputsthe ratio of the period of emitting said white light; and the ratio ofthe period of emitting the white light being adjusted based oninformation input to the input portion.
 6. The display device accordingto claim 1, the light source having light emitting portions that emitthe plurality of different color lights respectively.
 7. The displaydevice according to claim 6, the light emitting portion being a solidlight source.
 8. The display device according to claim 6, during theperiod of emitting said white light, the white light being emitted bysimultaneously emitting different color lights from the light emittingportions that emit the different color lights.
 9. The display deviceaccording to claim 6, the light source having a white light emittingportion that can emit the white light; and during the period of emittingthe white light, a white light being emitted from the white lightemitting portion.
 10. The display device according to claim 1, thedifferent color lights being sequentially emitted on a basis of a subunit period produced by dividing one unit period for producing an image;and the white light being emitted in a part of the sub unit period. 11.The display device according to claim 1, the different color lightsbeing sequentially emitted on a basis of a sub unit period produced bydividing one unit period for producing an image; and when the whitelight is emitted, a sub unit period for emitting the white light isadded to the unit period.
 12. The display device according to claim 11,the duration of the unit period being the same as the duration withoutthe additional sub unit period for emitting said white light.
 13. Thedisplay device according to claim 11, the duration of the sub unitperiods being the same regardless of the presence/absence of the subunit period for emitting the white light.
 14. The display deviceaccording to claim 1, the optical modulation device being a liquidcrystal panel.
 15. A displaying method using a display device, thedisplay device comprising: a light source capable of time-sequentiallyemitting a plurality of different color lights and a white light; anoptical modulation device that modulates light corresponding to thelights emitted from the light source; and a ratio of a period ofemitting the white light relative to a total of the periods of emittingthe lights from the light source being variable.
 16. A projection typedisplay device, comprising: a display device according to claim 1.